1. Field of the Invention
This invention pertains to the field of emergency power systems. More particularly, it pertains to a rotary dynamo device that is close-coupled to a flywheel to provide instant short-term alternating current, with maintained voltage regulation, to critical electric loads that may include frequency tolerant devices.
2. Description of the Prior Art
Commercial electrical power available today is becoming unreliable due to the growing number of electrical loads placed on the electrical power grid. In addition, many of the new loads on the power grid are critical in their need for constant frequency and/or voltage. These loads are usually tolerant of a small change in frequency, however, they cannot tolerate an instantaneous loss of power without concomitant damage.
For instance, some modern molding machines and metal-forming machines require constant power for sustained operation. They will tolerate only momentary and short-span variations in voltage and frequency, however, they cannot tolerate an unplanned, instantaneous, total loss of power. Should this occur, the molding machine will likely seize and possibly catch fire, from the high temperature material trapped in the mold, while the metal-forming machine will begin to spin down with the cutting tool remaining against the work piece and often will cause unplanned cutting on the work piece that destroys it. In the case of stand-alone computers and computer-driven machinery, the instantaneous and continuous loss of power may result in corruption of the computer files or loss of important program data.
Momentary electrical outages, frequency or voltage fluctuation (sags and spikes), extended outages and questionable return of normal power to an electrical load are thus becoming common place. These electrical power problems affect all governmental, commercial, industrial and private sectors of society. These locations that are affected include but are not limited to National Security, Law Enforcement, Hospitals, Communication, (cellular, paging services, satellite data recovery sites, local telephone service, microwave and antenna repeater sites), Radio and Television Broadcasting, Commercial Data Centers and any other electrical load supported or backed up by the commercial electric grid.
In order to ameliorate the potentially disastrous effects of such interruptions in commercial power to critical electric machines, an industry has grown up around a combination of electrical equipment that has, as its goal, the immediate implementation of supplemental alternating current to the electrical load. This supplemental alternating current must be frequency and voltage stable for a period of time varying from a few seconds, such as between about 8 seconds to 20 seconds, to a longer period, such as indefinitely or until the resumption of commercial power. In the short periods, such as 8 to 20 seconds, the critical machines enter a shut-down program designed to save the machine and the product produced by the machine. In longer periods, varying anywhere from 20 seconds to as much as hours or days, the load is serviced by the supplemental alternating current until the resumption of commercial power. In the case of the molding machines, the 8 to 20 second shut-down program would include the immediate opening of the mold and the expelling of the part being molded to free the machine from possible fire or lock-up by virtue of over-curing the material caught in the mold. In the case of metal-forming machines, the short shut-down program would be the immediate withdrawal of the cutting tool to preserve the work piece in its partially-formed configuration and then a shut down of the work piece drive motor. In the case of computers and computer-controlled machinery, the 8 to 20 second shutdown program would include the pre-programmed shut down of various subassemblies of the computer until the entire computer and processor are turned off resulting in saving data and preserving programs without corruption.
Prior art equipment and systems designed to provide this supplemental alternating current utilize batteries to provide direct current that is inverted to alternating current. The alternating current produced by this inverted battery power keeps the equipment running, while fault notices coming from power monitors, immediately switch the critical loads into their respective shutdown programs to allow the equipment to later go off-line and shut down in an orderly fashion thereby preserving the equipment, work pieces and computer programs and data. The reason batteries are used as the prime source of power is that inverting direct current to 60 Hertz alternating current from a battery can be accomplished with an inverter.
Unfortunately, battery-powered systems of this type are not popular for a number of reasons. First, batteries require a substantial capital investment that must be maintained by replacing batteries as they wear out, due to usage and just plain old age, usually on the average of every five years. Secondly, batteries are subject to boiling over, exploding, leaking, and other such maladies that require constant maintenance which raises the cost of having them in the power system. In addition, batteries must be located in ambient conditions that include a warm, dry atmosphere and this often requires a controlled environment, including heating and air conditioning equipment, that increases the overall cost of operation. Many manufacturing plants that need this type of protection are located in areas where harsh environmental conditions exist for at least part of the year. In these areas, batteries are not desired because these harsh conditions contribute to their instability and their early demise.
The devices of this small but growing industry are often referred to as Uninterruptible Power Supply (UPS) systems. During an outage, this system, supported by an array of direct current batteries or a flywheel apparatus that replaces the direct current battery array, provides direct current power that is transformed into alternating current and fed into the power grid load for a short period of time, such as for 8 to 20 seconds in order for the critical electric load to undergo an orderly shutdown. Batteries cannot provide sustained power because of their limited capacity. However, in some cases, such as in momentary interruption of commercial power, this battery-powered UPS system will continue the alternating power to the load until commercial power is restored if the interruption is for only for a short duration. In other cases, the UPS system can be modified to provide a prime mover, such as a fossil fuel-driven engine driving an electric generator, to provide continuous alternating current to the load during periods of extended outages. However, in all these cases, batteries are the source of the instantaneous power fed to the load. In addition, these prior art devices are special built and use parts that must be specially ordered and manufactured leading to high costs and long ordering and reordering delays.
Most electrical power grids have similar characteristics when they malfunction, including: sags (alternating current voltage decreases), surges (alternating current voltage increases), transients (alternating current voltage spikes caused by utility load sub-cycle switching), flickers or blinks (sub-second momentary alternating current voltage outage), momentary outages (alternating current voltage loss greater than 1 second) and extended outages (alternating current voltages loss for an undetermined amount of time). An Uninterruptible Power Supply system is designed to protect against all these abnormalities by eliminating the instantaneous loss, sags, or surges or of power (identified as "outage" throughout the balance of this patent application) and substituting it with short-duration power of similar frequency and voltage in order to allow pre-programmed shutdown.
The Uninterruptible Power Supply systems in the prior art are provided in two general designs: First, there is the Static UPS system that utilizes alternating current input and rectifies the electrical power to direct current. This direct current is used to charge the batteries for outage protection and supports the inverter to reconvert the direct current power to alternating current to supply the alternating electrical power for the load. Upon loss of input alternating current, the inverter is continuously supported by the direct current battery system until the battery system is depleted or normal alternating current is restored to the input of the Static UPS system. If the battery system is depleted prior to the restoration of normal alternating current power, the load will experience a loss of power and shutdown.
Second, the Rotary UPS system utilizes an input to support the motor section of the system that rotates an alternating current generator to supply electrical power to the load. The Rotary UPS system may be supported by the following systems to insure outage protection:
U.S. Pat. No. 4,243,598 discloses a direct current motor coupled directly to an alternating current motor and generator to maintain the nominal rotor shaft speed during an outage condition. The direct current motor is supported by a battery system as in the Static UPS system. It may also provide battery support for a Rotary UPS system.
U.S. Pat. No. 4,827,152 discloses a directly coupled hydraulic motor that utilizes a high pressure hydraulic bladder system to maintain rotor shaft speed long enough to allow an engine to start and support the system rotor shaft speed. When normal power is restored, the system will continue to operate on the engine until the hydraulic bladder is replenished and ready for another outage condition.
U.S. Pat. No. 5,811,960 discloses an alternating current generator coupled to a continuous power alternating current motor and further coupled to a flywheel to provide power to the systems internal direct current rectifier to support the rectifier when commercial input alternating current power is removed. The alternating current generator is connected to the rectifier section via a filtering inductor choke assembly that dampens the effects of power fluctuation on the output to the load. The commercial power flow bypasses the rectifier and inverter section. The rectifier and inverter operate in an energized standby mode with no load being supported by this section. Upon commercial power loss to the system, the rectifier is supported by the flywheel source providing direct current power to the inverter until it is replaced with direct current power from the emergency generator to support the inverter. Upon command from the system controller, the system internal inverter will synchronize the alternating current power from its output to the alternate source of the emergency generator and transfer the load from the inverter to the emergency generator. The emergency generator then supplies electrical power to the load until commercial power is restored and then re-transfers to commercial power via the filtering inductor assembly. The flywheel section must now be returned to normal speed via the alternating current drive motor and re-synchronized to the filtering inductor power to get ready for the next outage.
U.S. Pat. No. 4,707,774 discloses a high speed flywheel supported by a source of power provided by an inverter that is unsynchronized to the alternating current input source to support a direct current chopper circuit. The direct current chopper maintains a regulated voltage level of direct current to support the inverter circuit. The inverter circuit supplies the load with regulated and frequency controlled alternating current. Outage protection is supplied as long as the flywheel can provide electrical power to support the chopper or an alternating current source can restored to the input of the system.